Mechanism of As(III) removal properties of biochar-supported molybdenum-disulfide/iron-oxide system.

Sulfate (SO) and hydroxyl-based (HO) radical are considered potential agents for As(III) removal from aquatic environments. We have reported the synergistic role of SO and HO radicals for As(III) removal via facile synthesis of biochar-supported SO species. MoS-modified biochar (MoS/BC), iron oxide-biochar (FeO@BC), and MoS-modified iron oxide-biochar (MoS/FeO@BC) were prepared and systematically characterized to understand the underlying mechanism for arsenic removal. The MoS/FeOx@BC displayed much higher As(III) adsorption (27 mg/g) compared to MoS/BC (7 mg/g) and FeOx@BC (12 mg/g). Effects of kinetics, As(III) concentration, temperature, and pH were also investigated. The adsorption of As(III) by MoS/FeOx@BC followed the Freundlich adsorption isotherm and pseudo-second-order, indicating multilayer adsorption and chemisorption, respectively. The FTIR and XPS analysis confirmed the presence of Fe-O bonds and SO groups in the MoS/FeO@BC. Electron paramagnetic resonance (EPR) and radical quenching experiments have shown the generation of SO radicals as predominant species in the presence of MoS and FeO in MoS/FeOx@BC via radical transfer from HO to SO. The HO and SO radicals synergistically contributed to enhanced As(III) removal. It is envisaged that As(III) initially adsorbed through electrostatic interactions and partially undergoes oxidation, which is finally adsorbed to MoS/FeOx@BC after being oxidized to As(V). The MoS/FeO@BC system could be considered a novel material for effective removal of As(III) from aqueous environments owing to its cost-effective synthesis and easy scalability for actual applications.